Your DNS records have 1-day TTLs, so that's how long it can take for old data to clear out of caches.
$ dig www.fitnaturally.co.uk a @ns1.tsohost.co.uk +norec
; <<>> DiG 9.6-ESV-R4-P3 <<>> www.fitnaturally.co.uk a @ns1.tsohost.co.uk +norec
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 7116
;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;www.fitnaturally.co.uk. IN A
;; ANSWER SECTION:
www.fitnaturally.co.uk. 86400 IN A 79.170.44.156
86400 seconds is 1 day. I'm assuming you had the same TTL on the old record that this replaced.
If you want changes to propagate more quickly, you have to lower the TTL. Note that this has to be done BEFORE you make the change, since caches get the TTL when they look up the old data, and hold on to it for that long before checking again.
To answer the inevitable next question: no, there's no way to force caches to clear.